This invention relates to a heat-sensitive recording method and a thermal head, and more particularly to such a method and head which can print at high speed with excellent printing quality even onto a recording member having a rough surface.
Recently, according to the popularization of word processing and other heat-sensitive transfer equipment, heat sensitive recording methods using thermal heads, etc. to transfer the heat sensitive recording media (or ink material) to transfer media such as recording paper, etc. have been widely employed.
By the above-described heat-sensitive recording method using a thermal head, a part of the ink layer of the heat-sensitive recording medium is heated by a dot printing unit and is transferred to the transfer medium under pressure applied at the same time and then the supporting member of the heat-sensitive recording medium is separated, thereby the above-described part is transferred to the transfer medium.
In such heat-sensitive recording method, various devices have been made for the ink layer to improve the printing quality even for transfer media of low surface smoothness and heat-sensitive heads as follows have been proposed: a thermal head which is designed so that the above-described part is separated from the supporting means as quickly as possible by positioning the dot printing unit of the thermal head near the edge of the board, a thermal head positioned at a certain inclination angle to the transfer medium to increase the platen pressure, a thermal head in which a double glaze layer is formed projecting on the surface opposing to the heat-sensitive recording medium of the board and a heat resistant element is provided at the top of the double glaze layer, etc.
However, in every above-decribed thermal head, the part to be transferred is pressed strongly under pressure by the dot printing unit itself provided with a heat resistant element, and when pressed, the part to be transferred has been melted with very little cohesive power unable to hold its form so that bridging transfer onto concave-convex parts of the transfer medium becomes impossible. In addition, a crushed image is formed, melted ink soaks into paper fiber when the transfer medium is paper, and resultantly, paper fiber may come up to the surface from the image. Furthermore, a void or a blur may result or a stain of the base or trailing by the high temperature dot printing unit may result when it is pressed.
In order to solve the above problems, a heat sensitive recording medium with such an ink layer which has high cohesive power even at the time of transfer to the transfer medium should be used and resultantly, the shearing property at the border between the heated part to be transferred and an ink layer which has not been heated decreases due to the high cohesive power of the ink layer, deteriorating the printing sharpness.
Also in the high speed printing process, sufficient cooling time could not be secured to cool the dot printing unit because of the short pulse cycle of thermal energy and as the result, trailing or stain of the base was caused often in the conventional heat-sensitive heads in which the heat-sensitive head is always pressed strongly by the heat resistant element itself. In super-high-speed printing (80 cps for instance), due to the delay in the softening of the ink layer, effective pressing could not be applied in the printing.
This invention was made based on the above conditions.
That is, the object of this invention is to provide a heat-sensitive recording method and thermal head which can print with less generation of a void, blur, trailing, stain of the base, etc. even for transfer media of low surface smoothness, not to mention transfer medium of high surface smoothness, with high printing quality and especially at high speed.